joel at vnode.se
Wed Nov 16 15:04:10 UTC 2011
On 16-11-2011 16:33, Alexander Motin wrote:
> On 11/16/11 16:14, Bjoern A. Zeeb wrote:
> > On Wed, 16 Nov 2011, Alexander Motin wrote:
> >> Hi.
> >> On 11/16/11 08:43, Bjoern A. Zeeb wrote:
> >>> we have seen this or a very similar panic for about 1 year now once in
> >>> a while and I think I reported it before; this is FreeBSD as guest on
> >>> vmware. Seems it was a double panic this time. Could someone please
> >>> see what's going on there? It was on 8.x-STABLE in the past and this
> >>> is 8.2-RELEASE-p4.
> >> The part of code reporting "completing request directly" is IMHO broken
> >> by design. It returns request completion before request will actually be
> >> completed by lower levels without any knowledge of what's going on
> >> there. There is kind of protection against double request completion,
> >> but it looks like not always working. May be because that part of code
> >> is not locked and nothing prevents that semaphore timeout and normal
> >> request timeout/completion to happen simultaneously. It is surprising to
> >> see even two traps same time, not sure what synchronized them so
> >> precisely.
> >> Simple removing that semaphore timeout is not an option, because it will
> >> cause deadlock when this wait happen within taskqueue thread that is
> >> used to handle requests completion and abort that wait. Avoid waiting
> >> inside taskqueue is also impossible without major rewrite. That's why
> >> ATA_CAM drops that code completely.
> > So the bottom line of what you are saying is:
> > 1) it's hard to fix right in 8
> > 2) it's not an issue in 9 anymore at all?
Hmm. We're running many FreeBSD 8.2 machines as guests in VMware but have
never encountered the panic described above. Should I be worried? :-)
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